I don't think I can do a top 5 list. Uless I could magically change my size and weight and take a punch from each of the gus talked about there is no way I could really guess. A lot of hard itters in MMA. Hendo Lawler Carwin Lombard Liddell Gomi Though a note on Gomi, his swagger and his unbelievable aim did a lot for him. He threw punches surgically. Hunt of course without question is one of the hardest hitting imagineable. JDS is a hard hitter, but he is also in a way like Gomi. He is great at aiming for the specific ares he wants to hit. Igor without a doubt smashed faces. I think the straight left of Cro Cop is often overlooked as well.
5 strongest punchers huh? hmm lets see (My List) sergei Kharitinov , Jermey Stephens , Melvin Guillard , Anderson Silva , JDS = how'd i leave out Hendo, sorry some other names Blowjob Penn , Liddel , Rampage, etc
I guess a few of the guys mentioned let their skill sets erode and relied on their power later in their careers